The city’s teachers union is set to formally endorse Gov. Pataki’s re-election next Wednesday – making him the first Republican to be backed by the powerful union since Nelson Rockefeller, The Post has learned.

“People started being told last Friday that the decision has been made,” said one source with close ties to organized labor.

Another Democratic insider said that McCall’s camp was notified last week by United Federation of Teachers president Randi Weingarten.

McCall, Weingarten and Pataki yesterday all were mum about the endorsement vote next week.

Without saying she’s supporting Pataki, Weingarten told The Post she laid out the union’s endorsement process during a meeting with McCall last Friday.

“There’s a presumption to endorse the incumbent if he has a good record on education, labor and human-rights issues,” Weingarten said.

“The question is: Does the love of Carl McCall override the policy?”

After speaking at a breakfast sponsored by Crain’s New York Business, McCall said he wouldn’t talk about his conversation with Weingarten.

“I would hope that [the endorsement] wouldn’t happen, because I think that would be a disastrous signal to children that the union only cared about some deal that they’ve made,” McCall said.